Masters Theses


"In recent years there was a need for developing efficient NDE techniques for large area inspection. Conventional ultrasonic inspection techniques such as C-scan and B-scan are very time consuming because the transducer needs to be scanned over each point of structure under the test. Ultrasonically, Lamb Wave is considered to be a candidate for large area inspection based on its capability of propagating long distances and its media- thickness dependent propagation properties. Unfortunately, Lamb wave inspection is complicated by the existence of at least two modes at any given frequency. The modes are also highly dispersive in nature. As a result the flaw detection with these ultrasonic signals becomes highly complicated and the interpretation of the signals becomes very difficult and also leads to signal-to-noise problems. Consequently, a new kind of signal analysis is required to interpret the results of inspection and to determine if there is a defect or not. In order to extract the information on defects from the Lamb wave signal received by an ultrasonic transducer in such noisy environments, a method of analysis based on Wavelet Transforms is used. A Wavelet transform method has been developed for Lamb Waves generated in the aluminum plates and it showed a remarkable improvement in damage detection and reduced misdetections by a significant amount. The robustness of the technique was established by testing on various samples which include cracks, edge-disbonds, and sub-surface defects like grindouts. The method was able to detect all of the above damages with great accuracy. The wavelet analysis of the signals helped in developing a reliable Lamb Wave based damage detecting system for Health Monitoring of aging aircraft structures"--Abstract, page iii.


Rao, Vittal S.

Committee Member(s)

Chandrashekhara, K.
Okafor, A. Chukwujekwu (Anthony Chukwujekwu)


Mechanical and Aerospace Engineering

Degree Name

M.S. in Mechanical Engineering


The financial assistance provided in the form of Graduate Research Assistantship through grants from the United States Air Force and the Intelligent Systems Center is also gratefully acknowledged.

Research Center/Lab(s)

Intelligent Systems Center


University of Missouri--Rolla

Publication Date

Fall 2004


ix, 58 pages

Note about bibliography

Includes bibliographical references (pages 55-57).


© 2004 Rabindranath Gubbala, All rights reserved.

Document Type

Thesis - Restricted Access

File Type




Subject Headings

Lamb waves
Nondestructive testing
Wavelets (Mathematics)

Thesis Number

T 8687

Print OCLC #


Link to Catalog Record

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